The present invention broadly relates to the papermaking art, and, more specifically, concerns a new and improved construction of a papermaking machine containing two movable water pervious dewatering bands, for instance sieves or wires.
Generally speaking, the papermaking machine of the present development is of the type wherein one of the bands, the lower band, contains an essentially horizontally extending and substantially flat or planar section which is equipped with a headbox for the infeed of a fiber stock suspension onto the lower band. Additionally, there is provided a shoe having a domed or arched surface over which there is guided at least one of the bands, and a dewatering cylinder is arranged after the shoe. Both of the bands are conjointly guided over the dewatering cylinder along a portion of its circumference, and the shoe is arched or domed such that it posesses a larger radius of curvature than the dewatering cylinder.
A papermaking machine of this type is known in this art, for instance, from U.S. Pat. No. 4,176,005, granted Nov. 27, 1979. The double sieve or filter papermaking machine disclosed in the aforementioned U.S. Pat. No. 4,176,005--also sometimes referred to in the art as a twin-wire type of papermaking machine--affords a particularly favorable course of the dewatering of a fiber web which is formed upon one of the sieves or wires in that its intensity can be increased in steps or stages, initially at a flat or planar section, then at a section working with a suction action, a domed or arched shoe and finally at a dewatering cylinder. Additionally, at the region of the shoe and the dewatering cylinder there can be provided mechanical regulation expedients for the purpose of controlling the dewatering intensity.